Sandwich Construction Fin Mounting

ABSTRACT

Fin plug assemblies for mounting a removable watercraft fin are disclosed. In some embodiments the fin plug assemblies include a fin plug and a mounting insert, wherein the fin plug is configured to mount removable fins (e.g., surfboard fins) to a surface of a watercraft. In some embodiments, the mounting insert has a laminar or sandwich construction. Methods of manufacturing the fin plug assemblies and watercraft including the fin pug assemblies are also described.

FIELD OF THE INVENTION

This invention relates to watercraft and in particular to assemblies for removably securing fins to the watercraft.

BACKGROUND TO THE INVENTION

A number of watercraft make use of fins that project from the water-facing surface of the craft. On planing craft, such as surfboards, the fins are typically foil-shaped to enhance the directional stability of the craft during high speed planing motion and to facilitate turning.

The invention will be described with reference to surfboards as examples of watercraft, but it will be appreciated that the invention will find application in any watercraft that makes use of removable, replaceable fins that are mounted in a fin mounting assembly secured within a cavity formed in the water-facing surface of the craft.

On watercraft such as surfboards the use of removable fins has become quite commonplace. These fins are removably and interchangeably fitted to the watercraft by means of fin mounting systems embedded in the water-facing surface of the craft, the fin mountings typically having a cavity that is configured to receive the base of the fin. Various securement mechanisms are used to secure the fin base in the mounting system cavity.

In conventional surfboard manufacturing terminology, the fin mounting systems are referred to as fin plugs.

One of the problems encountered with known fin plugs arises from the characteristics of surfboard construction.

Surfboards are typically constructed from a relatively low-density foam core enveloped in a glass reinforced polyester resin skin laminated to the core. It will be appreciated that considerable torsional loads are imposed on the fin plug as a result of sideways thrust forces applied to the fin during use of the surfboard. In typical installations, the outer laminate of the surfboard is extended partially over the fin plug, but given the size limitations imposed by the locations where the fin plugs are installed on the surfboard, the laminate contact surface offered by the fin plug is generally insufficient to provide any real support to the fin plug in resisting the torsional loads imposed on the fin plug. The fin plug extends into the foam core of the surfboard and the fin plug is generally attached to the foam core by means of a suitable bonding agent, typically polyester resin which is conventionally used to laminate the surfboard. However, the low-density foam of the core generally does not have sufficient strength to resist the torsional fin plug loads without deformation or weakening of the surrounding foam over time, with consequential reduction in performance of the fin, cracking and shattering of the laminate in the vicinity of the fin plug and eventually delamination of the laminate from the core.

To overcome these problems, fin systems have been proposed that utilise a fin plug with a collar or flange extending about the open end of the fin-receiving cavity. The collar or flange upper surface is intended to stiffen the fin plug against side loads and to provide a bonding surface for the fibreglass laminate covering the fin plug. These fin plugs are typically of injection mouldable plastics, which generally does not bond well to the polyester resin most commonly used to laminate modern watercraft, unless the fin plug is treated, for instance by sanding, to provide some form of mechanical key and even this does little to improve bonding of the plastic to the resin. In addition, it will be appreciated that this introduces a secondary process that increases the cost and complexity of fin system installation.

It is an object of this invention to address these concerns.

SUMMARY OF THE INVENTION

According to this invention, a fin plug assembly for removably mounting a removable watercraft fin on a water-facing surface of a watercraft, the fin plug assembly includes:

-   -   a fin plug comprising a fin housing configured to house and         mount a mounting base of the watercraft fin;     -   a mounting insert having an insert body with operationally         water-facing and inwardly facing surfaces, the mounting insert         having a cavity formed in the water-facing surface that is         shaped complementally to and configured to receive the fin         housing;     -   the water-facing surface of the mounting insert being configured         for co-operation with the water-facing surface of the         watercraft;     -   the mounting insert body being configured for co-operation with         and mounting within a cavity previously formed in the         water-facing surface of the watercraft, the insert body shape         being complemental to the cavity shape; and     -   the mounting insert having a laminar construction.

In the preferred form of the invention, the mounting insert is configured with water-facing and inwardly facing surfaces separated from one another by a central core in which the material characteristics of the water-facing surface, the core and the inwardly facing surface are different.

The mounting insert could be all laminar in the sense that the entire insert, including the core, is made up in layers of material.

Alternatively, the laminar construction of the mounting insert can be achieved in a unitary insert body made from substantially the same material throughout in which the laminar structure is constituted by modification of the material characteristics of the core in and adjacent the water- and inwardly facing surfaces. In a foam body, for instance, the density of the foam can be varied as between the core and the two surfaces to achieve a laminar structure in which the foam at each surface is more dense and more rigid than the foam within the core.

In the preferred form of the invention, however, the laminar construction is achieved by using a laminated or sandwich construction for the insert body, with the water- and inwardly facing surfaces being constituted by different materials laminated to a core.

In this embodiment of the invention, either or both surfaces can be structural. In addition, the core could be structural. As an example, the mounting insert may comprise an insert body with a laminated construction including a core made from a high density foam, a laminate on the inwardly facing surface constituted by a relatively more rigid laminate and a laminate on the water-facing surface constituted by a load dissipating laminate.

In this form of the invention:

-   -   the core may conveniently be made from a high density foam, such         as polyurethane or PVC foam;     -   the laminate on the inwardly facing surface may be constituted         by a relatively rigid laminate and preferably one with a         three-dimensional cell structure, such as a SORIC™ laminate; and     -   the laminate on the water-facing surface may be constituted by a         load dissipating laminate, which may include anything from a         fibre reinforced resin sheet or laminate (such as a laminate         made from glass-, carbon- or synthetic fibre reinforced resin)         to wood veneer.

The fin plug may be a conventional injection moulded polycarbonate in which grub screws mount and lock the fin in place.

In the preferred form of the invention, however:

-   -   the fin plug is constituted by a fin plug sub-assembly         comprising a fin housing and a flange plate and the mounting         insert is constituted by a mounting insert body comprising a         number of laminated layers;     -   the fin housing having an externally cylindrical body, bulbous         cylindrical ends and bulbous fin-securing grub screw posts, the         external surfaces of which are part-circular;     -   the flange plate being configured for sandwiching between layers         of the mounting insert body and having an aperture formed         therein that is shaped complementally to accommodate the fin         housing;     -   the aperture in the flange plate having a surrounding aperture         wall that is cross-sectionally curved and shaped complementally         to accommodate the cross-sectionally curved cylindrical portions         of the fin housing to allow rotation of the fin housing within         and relative to the flange plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic isometric view of a fin plug assembly according to one embodiment of the invention;

FIG. 2 is a diagrammatic isometric view of a mounting insert forming part of the fin plug assembly of FIG. 1;

FIG. 3 is a diagrammatic exploded isometric view of the mounting insert of FIG. 2;

FIGS. 4 and 5 are diagrammatic isometric views illustrating a fin plug forming part of the fin plug assembly of FIG. 1;

FIG. 6 is a diagrammatic isometric view of a router jig for use in the installation of the fin plug assembly in a watercraft such as a surfboard;

FIG. 7 is a diagrammatic isometric view of a fin plug assembly according to a second embodiment of the invention;

FIG. 8 is a diagrammatic isometric view of a fin housing assembly including a fin plug and fin plug housing flange plate for the fin plug assembly of FIG. 7, viewed from above;

FIG. 9 is a diagrammatic isometric view of the assembly of FIG. 8, viewed from below;

FIG. 10 is a diagrammatic isometric view of the fin housing of FIG. 9;

FIG. 11 is a plan view of the fin housing of FIG. 10;

FIG. 12 is an under plan view of the fin housing of FIG. 10;

FIG. 13 is an end elevation of the fin housing of FIG. 10;

FIG. 14 is a diagrammatic isometric view of the fin housing flange plate for the fin plug assembly of FIG. 7, viewed from above;

FIG. 15 is a diagrammatic exploded isometric view of a top plate assembly for the fin plug assembly of FIG. 7;

FIG. 16 is a diagrammatic exploded isometric view of a core or bottom plate assembly for the fin plug assembly of FIG. 7;

FIG. 17 is a diagrammatic exploded isometric view of the fin plug assembly of FIG. 7; and

FIG. 18 is a diagrammatic isometric view of a router jig for use in the installation of the fin plug assembly of FIGS. 7 to 17 in a watercraft such as a surfboard.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Two embodiments of the invention are illustrated in the drawings, the first embodiment being illustrated in FIGS. 1 to 5 and the second embodiment being illustrated in FIGS. 7 to 17, with like elements of the second embodiment being numbered with like numbers except that the first embodiment elements are numbered from 10 onwards and to the second embodiment elements are numbered from 110 onwards.

The fin plug assemblies illustrated in the drawings are intended for use in surfboards and, in essence, comprise a fin plug 12, 112 which is mounted within a mounting insert 14, 114. The fin plug 12, 112 is used to mount removable surfboard fins to the underside or water-facing surface of the surfboard (not shown). The mounting insert 14, 14 has a laminar or sandwich construction in which the water- and inwardly facing surfaces have laminar sheets or plates 14.1, 14.3; 114.1, 114.3 respectively laminated to a core 14.2; 114.2.

Referring first to FIGS. 1 to 6, the fin plug assembly 10 illustrated in FIG. 1 comprises a fin housing constituted by a fin plug 12 mounted in a mounting insert 14. The fin plug 12 is used to mount a removable surfboard fin to the underside or water-facing surface of the surfboard (not shown). The mounting insert 14 has a laminar or sandwich construction in which the water- and inwardly facing surfaces have laminar sheets or plates 14.1, 14.3 laminated to a core 14.2.

In conventional construction, the fin plug is mounted in a cavity formed in the water-facing surface of the board and the adjacent foam core by means of a mechanical router. The fin plug is then attached to the foam core by means of a suitable bonding agent, typically the polyester resin conventionally used to laminate the fiberglass skin to the surfboard.

The fin plug 12, which is illustrated in more detail in FIGS. 4 and 5, is made from injection moulded polycarbonate, which has a high degree of structural integrity and durability.

The fin plug 12 serves as the primary receptacle for a surfboard fin (not shown) which, in use, is inserted into a channel 20 formed in the fin plug 12 and secured in place by means of grub screws 22. The grub screws 22 are screwed into threaded holes formed in grub screw tabs 24 and support posts 26 that extend laterally from the under surface of the fin plug and more specifically from the external side wall of the channel 20.

The channel 20 is oriented at a predetermined angle relative to the under surface of the surfboard to provide a surfboard fin mounted in the fin plug 12 with a corresponding cant angle. Different fin plugs 12 may be provided with channels 20 oriented at different cant angles.

The external upper surface of the fin plug 12 is provided with a plurality of stability tabs, two of which (28) are situated at the ends of the fin plug 12. The drawings illustrate a fin plug 12 with two additional stability tabs 30 located along the side of the fin plug 12. To enhance torsional stability, the stability tabs 30 each have a support post 32 extending laterally from the underside of the stability tabs 30 to the external side wall of the channel 20. The upper surfaces of the stability tabs 30 provide a convenient location for colour-coded dots 34 that serve as channel cant angle indicators.

A raised resin dam 36 projects above the external upper surface of the fin plug 12. During manufacture of the surfboard, the glass fibre laminate on the undersurface of the surfboard is simply extended over the dam formation 36 and then removed during finish sanding to ensure a flush surface at the line of contact between the glass fibre laminate and the upper surface of the dam formation 36.

To reduce the overall mass of the fin plug 12 and to increase stiffness, a bridging housing 38 is formed in the bottom of the channel 20. The bridging housing 38 is rebated by means of a pair of cutouts 40, further to reduce mass and increase stiffness.

Referring particularly to FIG. 3 it can be seen how the body of the mounting insert body is made up of a core 14.2, the upper and lower surfaces of which have an upper plate 14.1 and a base plate 14.3 laminated thereto, the upper plate 14.1 defining the water-facing surface of the mounting insert 14 and the base plate 14.3 defining the inwardly facing surface of the mounting insert 14.

In practice, the laminar construction is achieved by preparing a relatively large sheet or panel constructed with sheet material upper-14.1 and base-14.3 laminates sandwiched to a sheet material core 14.2. The panel is then cut into insert blanks that are machined to the correct (in this example oval) shape.

In the process of machining the insert 14, a cavity 42 is machined within the core 14.2. The shape of the cavity 42 is configured to be closely complemental to the external shape of the fin plug 12, so that the fin plug 12 is a relatively snug fit within the cavity 42, with the external undersurface of the channel 20 being a snug fit within a deeper channel 42.1 formed within the cavity 42 and in the grub screw tabs 24 and the support tabs 30 being a snug fit within shallower recesses 42.2 formed within the cavity 42.

The resultant, machined mounting insert 14 consists of a sandwich structure that is designed to dissipate lateral dynamic loads imposed on the surfboard and the surfboard foam core in particular, by the surfboard fin during use.

In applications where the core 14.2 is essentially non-structural, serving largely to separate the upper plate 14.1 from the base plate 14.3, the core 14.2 is most commonly made from a high density foam, such as polyurethane or PVC foam. Other non-structural core materials, such as balsa wood can also be used. Alternatively, and particularly in applications where the core 14.2 use intended to be structural, the core 14.2 can itself be a laminar structure that is built up from multiple layers of suitable materials.

The base plate 14.3 (the laminate on the inwardly facing surface) is primarily responsible for dissipating lateral forces applied to the channel 20 by the surfboard fin.

In this regard, the upper perimeter of the fin plug channel 20 serves largely as a pivot for the surfboard fin and as a result surfboard fin loads are largely torsional.

At the bottom of the channel 20, however, large compression loads are generated by the base of the fin against the sidewalls of the channel, hence the loads at the bottom of the channel are relatively higher than the torsional loads applied to the top of the channel 20. To accommodate the relatively high loads, the base plate 14.3 is preferably of laminar construction, the preferred laminate being a cellular core with its thin layers on either side. An example of such a laminate is SORIC™ supplied by Lantor BV, Netherlands. SORIC™ is a polyester nonwoven material with a compression resistant hexagonal cell structure in which pressure-resistant hexagonal cells that contain synthetic micro-spheres, are separated by channels. The cells do not absorb resin and therefore limit the total resin up-take. The cells are pressure resistant and create thickness in the laminate. The channels facilitate resin flow and form a pattern of cured resin with good mechanical properties and excellent bonding to the core 14.2 and to the foam core of the surfboard.

The upper plate 14.1 (the laminate on the water-facing surface of the fin mounting insert 14) is preferably constituted by a relatively flexible load dissipating laminate that is capable of transferring the substantially torsional loads imposed by the surfboard fin on the upper perimeter of the channel 20 throughout the body of the insert 14. Suitable materials include anything from fibre reinforced resin sheets or laminates (such as a laminate made from glass-, carbon- or synthetic fibre reinforced resin) to wood veneer.

Besides being structural, the laminate on the water-facing surface may be at least partly cosmetic, since this laminate will be visible through the fiberglass laminate making up the external skin of the undersurface of the surfboard after installation of the fin plug assembly 10 in the surfboard.

The outer shape of the fin plug assembly 10 can be any desired shape and is not necessarily limited to the shape illustrated in the drawings. In each case an appropriately shaped router jig is required to rout the cavity in the surfboard to receive the fin plug assembly 20 during the surfboard lamination process. An example of such a router jig 44 is illustrated in FIG. 6. The jig 44 serves as a guide for a router bit equipped with a bearing at the top of the cutter that allows the router bit to follow the inner shape of the jig 44 to produce the desired cavity.

An example of the process of installing the fin plug assembly 10 of the invention is as follows.

The grub screws 22 are screwed fully into the grub screw holes and masking tape is applied to the dam 36 to seal off the channel 20 and to close off the grub screw holes.

The router jig 44 is placed on the shaper's marks on the surfboard and using a router bit with the correct bearing and depth, a cavity is routed in the surfboard to accommodate the fin plug assembly 10 with a snug fit as described above.

Polyester resin is poured into the cavity routed into the surfboard and the fin plug assembly 10 is pushed firmly into the cavity until fully seated within the cavity in the surfboard. Care must be taken to ensure that the empty spaces between the fin plug assembly 10 and at the surfboard cavity as well as the empty spaces within the fin plug assembly 10 (the spaces between the cavity 42 and the fin plug 12) are completely filled with laminating resin.

The glass fibre laminate making up the underside of the surfboard is laminated over the entire fin plug assembly and once set, the glass fibre covering the fin plug assembly 10 is sanded down to expose the resin dam 36, the open channel 20 and the grub screws 22. The fin plug assembly 10 is now ready for use and for the installation of a surfboard fin therein.

Referring to FIGS. 7 to 18, the fin plug assembly 110 illustrated in FIG. 7 comprises a fin housing constituted by a fin plug 112 mounted in a mounting insert 114. The mounting insert 114 has a laminar or sandwich construction in which the water- and inwardly facing surfaces have laminar sheets or plates laminated to a core 114.2.

The fin plug 112, which is illustrated in more detail in FIGS. 10 to 13, is made from injection moulded polycarbonate.

The fin plug 112 serves as the primary receptacle for a surfboard fin (not shown) which, in use, is inserted into a channel 120 formed in the fin plug 112 and secured in place by means of grub screws 122. The grub screws 122 are screwed into threaded holes formed in grub screw posts 124.

The fin plug assembly 110 differs from the fin plug assembly 10 in a number of ways.

The cant angle of the fin plug 112 not fixed by the angle determined during the manufacturing process. The cant angle of the fin plug 112 is infinitely adjustable by rotation of the fin plug 112, as will be described below.

In addition, the fin plug 112 dispenses with the stability tabs of the fin plug 12, the fin plug 112 being mounted in a mounting insert 114 in a fin housing assembly including the fin plug 112 and a fin plug housing flange plate 150.

The flange plate includes a substantial peripheral flange formation 151 that is shaped complementally to the external shape of the mounting insert 114 and configured to be sandwiched between between a top plate 114.1 and the core 114.2 of the mounting insert 114 during assembly where it provides rollover strength to the fin plug assembly 110, the flange 151 of the flange plate 150 serving to dissipate torsional loads across the insert core 114.2.

The flange plate 150 is formed with a central aperture 152 that is shaped complementally to the external contours of the fin plug 112. As will be described below, the flange plate aperture allows rotation of the fin plug 112 relative to the flange plate 150.

The mounting insert 114 is comprised of a sandwich construction including a top plate 114.1. As illustrated in FIG. 15, the top plate 114.1 may include a top plate core 114.4 made from a high density foam or any other machineable stable material, for example balsa wood. The material can be used for decorative as well as structural properties. As illustrated in FIG. 15, the core does not need to be a homogenous piece of material, but can be both a part of multiple layers of suitable material. In FIG. 15, the top plate 114.1 is shown to include a top plate overlay 114.5 that can be used to serve as a lateral load dissipating mechanism and a bonding surface. In most instances, the top plate overlay 114.5 will be made of glass reinforced polyester. However, any material can be used that is stiff and has good bonding properties for the bottom laminate of the surfboard. This could be anything from a wood than the active carbon fibre. It can also serve a decorative role when different materials are used for the overlay 114.5.

An opening 114.6 is machined into the top plate 114.1 to accept the flange plate 150. The top plate 114.1 could also be shaped to match the bottom contours of the surfboard should this be required.

The mounting insert 114 is completed by a core 114.2, illustrated in FIG. 16. The core 114.2 is responsible for dissipating lateral forces applied to the fin plug 112 by the surfboard fin. Because torsional loads at the bottom of the fin plug channel are typically higher than at the surface of the fin plug 112, the core 114.2 is thicker than the top plate 114.1.

The core 114.2 is machined with a central aperture 114.6 that is shaped complementary to the fin plug 112 the flange plate 150 such that the fin plug 112 and flange plate 150 are accommodated with a reasonably snug fit within the the aperture 114.6.

To accept and dissipate the loads applied to the core 114.2, the core is preferably constituted by a high density foam or a hard material like balsa wood. The core 114.2 need not be homogenous and can be built up part of multiple layers of suitable materials.

In the drawings, the core 114.2 is finished by a bottom plate 114.3 made from fiberglass, carbon fibre or a hexagonal core material. The bottom plate 114.3 creates a complete sandwich structure that serves to dissipate torsional loads applied to the fin plug assembly 110.

FIGS. 10 to 13 illustrate the fin plug 112. In essence, the fin plug 112 is the primary part of the fin plug assembly 110. It provides the primary receptacle for the fin base (the channel 120) as well as the mechanism for locking the fin in place (the grub screws 122).

More importantly, however, is the fact that the fin plug 112 is designed to deliver a wider range of fin cant angles by being able to rotate within the flange plate 150. To this end, the fin plug 112 is provided with an externally cylindrical body 112.1, bulbous cylindrical ends 112.2, and bulbous grub screw posts 124, the external surfaces of which are part-circular.

The aperture 152 in the flange plate 150 is formed with a surrounding aperture wall 154 that is cross-sectionally curved to accommodate the cross-sectionally curved cylindrical portions of the fin plug 112 and to allow rotation of the fin plug 112 within and relative to the flange plate 150.

The fin plug assembly 110 is assembled by first snapping the fin plug 112 into the flange plate 150 and then rotating the fin plug 112 to the desired fin cant angle, whereupon the fin plug 112 is glued in place within and relative to the flange plate 150. The flange plate 150 and fin plug 112 sub-assembly is then glued into the core 114.2 and bottom plate 114.3 sub-assembly. Finally, the top plate 114.1 is glued on top of the flange plate 150, sandwiching the flange plate 150 and fin plug 112 sub-assembly within the fin plug assembly 110.

The fin plug assembly 110 may be shipped fully assembled to allow installation of the fin plug assembly 110 into a surfboard with a single routing operations using the routing jig illustrated in FIG. 18. It is of course also possible to produce and deliver fin plug assemblies 110 in which the fin plug 112 is not fixed during assembly, thereby allowing a custom builder to find June the fin cant angle during the process of installing the fin plug assembly 110 in a surfboard.

The key advantage provided by the fin plug assembly 110 is the ability to provide a wide range of cant angles without the need for producing multiple fin plugs and fin plug moulds, each with a pre-set cant angle. Modern surfboard fin systems are required to allow the surfboard manufacturer to maximise the performance of fin set up, particularly the fin cant angle. In the past this has been achieved by the production of a multiplicity of fin plugs and fin plug moulds, each with a pre-set cant angle. The fin plug assembly 110, however, makes it possible to produce and provide a wide range of cant angles, anything between 0° to 10°, using a single fin plug 112. In addition, the fin plug assembly 110 provides surfboard designers and manufacturers with the ability to customise the fin cant angle during installation of the fin plug assembly 110 into the surfboard at the time of surfboard manufacture. The fin cant angle cannot be changed post-installation of the fin plug assembly 110 into the surfboard.

Aside from the dam and grub screw posts 124 of the fin plug assembly 110, the remaining details of the fin plug assembly 110 and installation thereof are similar to the specific features of the fin plug assembly 10 described with reference to FIGS. 1 to 5 and the description of such specific features apply equally to the fin plug 112 and mounting insert 114.

Instead of the raised resin dam 36 of the fin plug 12, the cylindrical body 112.1, 112.2 and the semi-cylindrical grub screw posts 124 project above the top plate 114.1 in the assembled fin plug assembly 110 to constitute a similar resin dam. However, the cylindrical raised surfaces of the fin plug 112 simplify draping of the resin-impregnated cloth over the fin plug assembly 110 and minimise air bubble formation during the surfboard lamination process. The glass fibre laminate on the undersurface of the surfboard is removed during finish sanding, together with the protruding portions of the fin plug 112. This ensures a flush surface at the line of contact between the glass fibre laminate and the upper surface of the fin plug 112.

In the fin plug 112, the grub screw posts are circular in cross-section to allow rotation of the grub screw posts with the fin plug 112 when it is set to the correct cant angle within the flange plate 150. The grub screw posts 124 are sanded flush with the surface of the underside of the laminated surfboard during finish sanding—the grub screws 122 are removed during finish sanding.

In the majority of the examples described herein, the fin plug assembly 10, 110 is a typical surfboard fin plug assembly, but this is not intended to restrict the invention to surfboards and in this regard, the terms “fin plug” and “fin plug assembly” must be given a wider interpretation so as not to restrict the invention to surfboard fin plugs and fin plug assemblies or to the fin plug assembly illustrated in the drawings. 

1. A fin plug assembly for removably mounting a removable watercraft fin on a water-facing surface of a watercraft, the fin plug assembly including: a fin plug comprising a fin housing configured to house and mount a mounting base of the watercraft fin; a mounting insert having an insert body with operationally water-facing and inwardly facing surfaces, the mounting insert having a cavity formed in the water-facing surface that is shaped complementally to and configured to receive the fin housing; the water-facing surface of the mounting insert being configured for co-operation with the water-facing surface of the watercraft; the mounting insert body being configured for co-operation with and mounting within a cavity previously formed in the water-facing surface of the watercraft, the insert body shape being complemental to the cavity shape; and the mounting insert having a laminar construction.
 2. The fin plug assembly of claim 1 in which the mounting insert comprises an insert body with a laminated construction including a core made from a high density foam, a laminate on the inwardly facing surface constituted by a relatively more rigid laminate and a laminate on the water-facing surface constituted by a load dissipating laminate.
 3. The fin plug assembly of either of the preceding claims in which: the fin plug is constituted by a fin plug sub-assembly comprising a fin housing and a flange plate and the mounting insert is constituted by a mounting insert body comprising a number of laminated layers; the fin housing having an externally cylindrical body, bulbous cylindrical ends and bulbous fin-securing grub screw posts, the external surfaces of which are part-circular; the flange plate being configured for sandwiching between layers of the mounting insert body and having an aperture formed therein that is shaped complementally to accommodate the fin housing; the aperture in the flange plate having a surrounding aperture wall that is cross-sectionally curved and shaped complementally to accommodate the cross-sectionally curved cylindrical portions of the fin housing to allow rotation of the fin housing within and relative to the flange plate. 